A user interface (below called a UI) is known which displays various operation keys on a display apparatus which uses liquid crystal, etc., to accept user operations via a touch panel and a pointing device. A PC (Personal Computer) which uses the display apparatus having a relatively large number of pixels can display a large number of operation keys on one screen, so that the need for effective utilization of the screen is not great. On the other hand, embedded-type apparatuses, for example, have a constraint that a size of the display apparatus cannot be made sufficiently large while the number of operation keys that are desired to be displayed on one screen is increasing with diversification of functions. The embedded-type apparatuses includes, for example, a printer, a copying machine, a facsimile apparatus, a scanner apparatus, an MFP with one of more of these functions installed (below called an image forming apparatus), a navigation apparatus, a mobile telephone, etc.
As a large number of operation keys are arranged in a limited display area while maintaining a UI which is easy to use for the user, each manufacturer devises the size and an arrangement of the operation keys; however, it may be physically difficult to display, on one screen, all of the operation keys which can be operated by the user.
Moreover, even when all of the operation keys which can be operated by the user can be displayed on one screen, only some of the operation keys correspond to functions often used by the user, so it is often the case that it is not necessary to display all of the operation keys which can be operated by the user.
Thus, a display apparatus is known such that each user can customize the UI (see Patent document 1, for example). Patent document 1 discloses an image forming apparatus which displays a list of operation keys corresponding to functions which can be arranged on a screen, and arrange an operation key selected from the list by a user at a desired location for customizing.